Runners' mighty quads and glutes reach long-mileage readiness well ahead of the smaller muscles in the feet and ankles. Yet this supporting cast plays a key role in achieving peak endurance. "Working the muscles in your feet develops your ability to transfer energy from the landing to the push-off, which helps you go farther with less fatigue," says Penny Hamilton, a Colorado-based personal trainer. "Plus, it develops the muscle control you need to prevent overuse injuries from high-mileage workouts." These exercises force the foot and ankle to continuously engage, which develops strength. Do them twice a week, preferably two days after speedwork or long-mileage runs. Once you're comfortable with the movements, try performing the exercises without shoes to challenge the feet even further.

Single-Leg Directional HopsImproves ankle and knee stability for a stronger push-off and landing.To Do: Standing on your left leg, with the right knee raised to hip height, hop forward, landing softly. Hop back to start, then hop diagonally (to the left) and back to center, hop to the left and return to start. Do 12 reps; switch legs.

Three-Point LungesDevelops energy transfer from landing to push-off; strengthens the lateral knee muscles for improved stability.To Do: Lunge the left leg forward. With quick force, push the left foot off the floor and into a diagonal lunge to the left, keeping the hips straight. Push the left foot off the floor again, landing in a lunge to the left side, keeping the upper body stacked over the hips. That's one rep. (Each rep should take about three seconds to complete.) Do six reps; switch legs.

Squat JacksBuilds strength from the feet up through the hips for better transfer of power.To Do: Standing in the bottom of a squat position with feet hip-width apart and shoulders stacked over hips, shoot your legs out to the sides and your arms out to shoulder height (like a regular jumping jack) without moving your upper body. Do 16 to 24 reps.

Single-Leg Mountain ClimbersStrengthens foot-strike muscles; engages hip flexors, quads, glutes, and core.To Do: Starting in a plank position, with abs engaged, bend your left knee and pin it against the right knee. Hop your right foot forward to waist distance, landing lightly on the ball of your foot and keeping the left leg from touching the ground. Then, shoot the right foot back, keeping knees pinned and left leg raised. That's one rep. Do 16 reps; switch legs.